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Why is it that a waterfall never runs out of water?

Have you ever seen a waterfall in real life? Then you must have noticed a lot of water falls down. All day, every day! Does that water never run out?

Rain

Water that enters the atmosphere always evaporates from the oceans. Then clouds arise and it starts to rain. The water first flows through small streams and eventually ends up in a river. It then returns to the ocean via the river, with a waterfall, for example. So the water in the ocean never runs out and the circle is closed: the water can evaporate again and bring new rain over land.

Drought

However, it does happen that waterfalls stop. In warm countries, such as Spain, it is so hot in summer and so little rain falls that some rivers run dry. The falls therefore stop until it starts raining again in the fall.